Method and apparatus for transceiving a data frame in a wireless lan system

ABSTRACT

A method of transmitting a data frame by a transmitter in a WLAN system is provided. The method includes generating a data block including at least one data units respectively transmitted through at least one or more spatial streams to at least one receiver, transmitting first control information to the at least one receiver, transmitting second control information to each receiver, and transmitting the data block to the at least one receiver. The first control information includes a length indicator for the data block, a MIMO indicator indicating whether the data block is for SU-MIMO or MU-MIMO, and a spatial stream indication field including information about the number of the spatial streams. The second control information includes a FEC coding field indicating an encoding scheme applied to the data unit and an MCS field indicating an MCS applied to the data unit.

TECHNICAL FIELD

The present invention is related to a wireless local area network (WLAN)system, and more specifically, to a method of transmitting and receivingdata frames by an access point (AP) and a station (STA).

BACKGROUND ART

Recent advance in information communication (IT) technologies leads todevelopment of various wireless communication technologies. Amongothers, WLAN is a technology that is based on a wireless frequencytechnology and that allows for wirelessly accessing the Internet in ahome or a specific service providing area by using portable terminalssuch as personal digital assistants (PDAs), laptop computers, andportable multimedia players (PMPs).

To overcome a weakness of WLAN, i.e., limited communication speed, theIEEE 802.11n standard has been recently established. This standardtargets increasing network speed and reliability as well as expandingthe operation range of the wireless network. Specifically, the IEEE802.11n supports a high throughput (HT) in which data processing speedreaches up to 540 Mbps and is based on the MIMO (Multiple Inputs andMultiple Outputs) technology in which a multi-antenna is used in each ofthe transmit unit and the receive unit so as to optimize data rate whileminimizing transmission errors.

As WLAN is spreading over and over and various applications using thisare developed, demand for new WLAN systems, which may support a higherdata processing rate than that supported by IEEE 802.11n, is growing up.The next-generation WLAN system supporting very high throughput (VHT) isa subsequent version of 802.11n WLAN and is one of new IEEE 802.11 WLANsystems as recently suggested to support a data processing rate of 1Gbps or more in the MAC service access point (SAP).

A next-generation WLAN system backs up MU-MIMO (Multi User MultipleInput Multiple Output)-based transmission in which a plurality of STAsattempts to simultaneously access the channel in order to efficientlyuse wireless channels. In such MU-MIMO transmission scheme, an AP maytransmit packets to one or more MIMO-paired STAs at the same time.

As various communication services such as smart grid, e-Health, andUbiquitous are introduced, M2M (Machine to Machine) technologies gainpopularity to support the services. A sensor for sensing temperature ormoist, a camera, a home appliance such as TVs, a processing machine usedin the factory, or vehicles or other large-scale machines may be anelement constituting an M2M system. The elements constituting an M2Msystem may attend data transmission and receipt based on WLANcommunication.

An M2M supportive WLAN system may be specified to use a frequency bandother than the existing frequency band used for data transmission andreceipt. In contrast to a conventional system using a band of 5 GHz, aWLAN system supporting M2M may be set to use a band of 900 MHz.

As configuring an M2M supportive WLAN system, a wireless apparatus usesa frequency band not to overlap the frequency band supported by theexisting WLAN system, and thus, may generate and transmit a data frame,i.e., PPDU (PLCP (Physical Layer Convergence Procedure) Protocol DataUnit), without considering backward compatibility. In other words, it isnot required to support compatibility with legacy stations (STAs) thatoperate in the existing WLAN system. Accordingly, when controlinformation for legacy STAs is, upon transmission, included in PPDU inaccordance with the existing PPDU transmission/reception scheme,overhead may occur unnecessarily. Therefore, there is a need for animproved PPDU transmission and reception method that may supportefficient data exchange in an M2M supportive WLAN system.

DISCLOSURE Technical Problem

An object of the present invention is to provide a data frametransmission method for supporting data exchange in a new frequency bandin a WLAN system and an apparatus supporting the same.

Technical Solution

In an aspect, a method of transmitting a data frame by a transmitter ina WLAN system is provided. The method includes generating a data blockincluding at least one or more data units respectively transmittedthrough at least one or more spatial streams to at least one or morereceivers, transmitting first control information to the at least one ormore receivers, wherein the first control information includes a lengthindicator for the data block, a multiple input multiple output (MIMO)indicator, and a spatial stream indication field, wherein the MIMOindicator indicates whether the data block is for SU (single user)-MIMOor MU (multi user)-MIMO, wherein the spatial stream indication fieldincludes information about the number of the spatial streams,transmitting to each receiver second control information, wherein thesecond control information includes a forward error correction (FEC)coding field indicating an encoding scheme applied to the data unit anda modulation and coding scheme (MCS) field indicating an MCS applied tothe data unit, and transmitting the data block to the at least one ormore receivers.

When the MIMO indicator indicates that the data block is transmitted byMU-MIMO transmission, the spatial stream indication field may include atleast one or more subfields, each subfield indicating a number ofspatial streams assigned to each receiver for transmitting each dataunit.

When the MIMO indicator indicates that the data block is transmitted byMU-MIMO transmission, the spatial stream indication field may be set toan index value mapped with information indicating the number of spatialstreams assigned to each receiver for transmitting each data unit.

The FEC coding field may indicate one of BCC (Binary Convolution Coding)encoding and LDPC (Low Density Parity Check) encoding.

The method may further include transmitting a training sequence used forestimating a MIMO channel between the transmitter and at least onereceiver before transmitting the second control information and aftertransmitting the first control information.

The length indicator may indicate duration required to transmit the datablock.

The second control information may further include a second lengthindicator for the data block.

A length of each data unit may be defined by a combination of a bitsequence constituting the length indicator and a bit sequenceconstituting the second length indicator.

In an aspect, a wireless device is provided. The wireless deviceincludes a transceiver transmitting and receiving a data block and aprocessor operatively coupled with the transceiver, wherein theprocessor is configured for generating a data block including at leastone or more data units respectively transmitted through at least one ormore spatial streams to at least one or more receivers, transmittingfirst control information to the at least one or more receivers, whereinthe first control information includes a length indicator for the datablock, a multiple input multiple output (MIMO) indicator, and a spatialstream indication field, wherein the MIMO indicator indicates whetherthe data block is for SU (single user)-MIMO or MU (multi user)-MIMO,wherein the spatial stream indication field includes information aboutthe number of the spatial streams, transmitting to each receiver secondcontrol information, wherein the second control information comprising aforward error correction (FEC) coding field indicates an encoding schemeapplied to the data unit and a modulation and coding scheme (MCS) fieldindicating an MCS applied to the data unit, and transmitting the datablock to the at least one or more receivers.

Advantageous Effects

The present invention suggests a format including control informationrequired in a new WLAN system supporting an M2M (Machine to Machine)application except for control information required fortransmission/reception of frames in a legacy station (L-STA) in a WLANsystem not supporting part of backward compatibility. Since data framesare subjected to transmission and reception with unnecessary legacycontrol information excluded, unnecessary overhead may be prevented frombeing generated.

A format as suggested includes a signal field including controlinformation to be able to support MU-MIMO (Multi User-Multiple InputMultiple Output) transmission. Through the MU-MIMO transmission, theoverall throughput of the M2M supportive WLAN system may be enhanced.

In the MU-MIMO transmission, a signal field is provided includingdifferent sub signal fields, one of which contains common controlinformation commonly required for a plurality of MU-MIMO paired STAs andanother of the sub signal fields containing dedicated controlinformation required for each STA. For this, STAs targeted fortransmission may receive all of the common/dedicated control informationand data and may perform data exchange, and other STAs may determinethat data is not the data therefor through the common controlinformation only. By doing so, the STAs may enhance power managementefficiency which is an issue of M2M.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a configuration of a wireless local areanetwork (WLAN) system according to an embodiment of the presentinvention.

FIG. 2 is a view illustrating a physical layer architecture of a WLANsystem supported by IEEE 802.11.

FIG. 3 is a view illustrating an exemplary PPDU format used in a WLANsystem.

FIG. 4 shows a PPDU format that may be applicable to an embodiment ofthe present invention.

FIGS. 1 to 33 are views illustrating examples of a signal field formataccording to an embodiment of the present invention.

FIG. 34 is a view illustrating an example of implementing lengthindication information that may be applicable to an embodiment of thepresent invention.

FIG. 35 is a view illustrating another example of implementing lengthindication information that may be applicable to an embodiment of thepresent invention.

FIG. 36 is a view illustrating an example of a Tx procedure based on aPPDU format according to an embodiment of the present invention.

FIG. 37 is a view illustrating an example of an Rx procedure for a PPDUgenerated according to an embodiment of the present invention.

FIG. 38 is a block diagram illustrating a wireless device to which anembodiment of the present invention may be applicable.

MODE FOR INVENTION

FIG. 1 is a view illustrating a configuration of a wireless local areanetwork (WLAN) system according to an embodiment of the presentinvention.

Referring to FIG. 1, the WLAN system includes one or more basic servicesets (BSSs). The BSS is a set of stations (STAs) which may communicatewith each other in successful synchronization with each other and is nota concept indicating a specific area.

An infrastructure BSS includes one or more non-AP stations non-AP STA1,non-AP STA2, non-AP STA3, non-AP STA4, and non-AP STA5, access points(APs) providing a distribution service, and a distribution system (DS)connecting the plurality of APs to one another. In the infrastructureBSS, an AP manages non-AP STAs in the BSS.

On the contrary, an independent BSS (IBSS) is a BSS operating in anAd-Hoc mode. The IBSS does not include any AP and thus lacks acentralized management entity. That is, in the IBSS, non-AP STAs aremanaged in a distributed manner. In the IBSS, all the STAs may beconstituted of mobile STAs and are not permitted to access the DS, thusconstituting a self-contained network.

The STA is any functioning medium including medium access control (MAC)following the IEEE (Institute of Electrical and Electronics Engineers)802.11 standard and a physical layer interface for a wireless medium,and in the broad concept includes both AP and non-AP station.

The non-AP STA is an STA that is not an AP. The non-AP STA may bereferred to by other names such as mobile terminal, wireless device,wireless transmit/receive unit (WTRU), user equipment (UE), mobilestation (MS), mobile subscriber unit or simply user. For ease ofdescription, the non-AP STA is hereinafter referred to as STA.

The AP is a functioning medium providing access to the DS via a wirelessmedium for an STA associated with the AP. In the infrastructure BSSincluding the AP, communication between STAs is basically performed viathe AP, but when a direct link is established, direct communicationbetween the STAs may also be possible. The AP may be also called centralcontroller, base station (BS), node-B, BTS (Base Transceiver System) orsite controller.

A plurality of infrastructure BSSs including the BSSs shown in FIG. 1may be connected to one another through a distribution system (DS). Theplurality of BSSs connected to one another through the DS is referred toas an extended service set (ESS). APs and/or STAs included in the ESSmay communicate with each other, and in the same ESS, an STA may shiftfrom one BSS to another BSS while maintaining seamless communication.

In the WLAN system following the IEEE 802.11 standard, a basic accessmechanism of MAC (Medium Access Control) is a CSMA/CA (Carrier SenseMultiple Access with Collision Avoidance) mechanism. The CSMA/CAmechanism is also called distributed coordination function (DCF) of IEEE802.11 MAC and basically employs “listen before talk” access mechanism.According to such type of access mechanism, an AP and/or an STA, beforeinitiating transmission, senses a wireless channel or medium. As aresult of the sensing, if the medium is determined to be in an idlestatus, packet transmission is started through the corresponding medium.In contrast, when the medium is determined to be in an occupied status,the corresponding AP and/or STA sets a delay period for medium accesswithout initiating its own transmission and stands by.

The CSMA/CA mechanism includes virtual carrier sensing as well asphysical carrier sensing for the AP and/or STA to directly sense themedium. The virtual carrier sensing is to compensate for a problem thatmay occur involving medium access such as hidden node problems. Forpurposes of virtual carrier sensing, the WLAN system uses a networkallocation vector (NAV). The NAV is a value by which an AP and/or STA touse a current medium or to have a right to use the current mediumindicates a time remaining until this medium turns into a usable statusto another AP and/or STA. Accordingly, the value set as the NAVcorresponds to a period during which the medium is scheduled to be usedby the AP and/or STA transmitting the corresponding packet.

The IEEE 802.11 MAC protocol, together with the DCF, provides an HCF(Hybrid Coordination Function) that is based on a PCF (PointCoordination Function) of periodically performing polling so that allthe receiving APs and/or STAs may receive data packets by apolling-based synchronous access scheme and the DCF. The HCF has HCCA(HCF Controlled Channel Access) using non-competition-based channelaccess scheme using a polling mechanism and EDCA (Enhanced DistributedChannel Access) using competition-based access scheme for a provider toprovide multiple users with data packets. The HCF includes a mediumaccess mechanism for enhancing QoS (Quality of Service) of WLAN and maytransmit QoS data during both a contention period (CP) and acontention-free period (CFP).

FIG. 2 is a view illustrating a physical layer architecture of a WLANsystem supported by IEEE 802.11.

The physical layer (PHY) architecture of IEEE 802.11 consists of a PLME(PHY Layer Management Entity), a PLCP (Physical Layer ConvergenceProcedure) sublayer 210, and a PMD (Physical Medium Dependent) sublayer200. The PLME cooperates with an MLME (MAC Layer Management Entity) andprovides a function of managing the physical layer. The PLCP sublayer210 transfers an MPDU (MAC Protocol Data Unit) received from an MACsublayer 220 to a sublayer according to an instruction of the MAC layerbetween the MAC sublayer 220 and the PMD sublayer 200 or transfers aframe coming from the PMD sublayer 200 to the MAC sublayer 220. The PMDsublayer 200 is a PLCP lower layer and enables a physical layer entityto be transmitted/received between two stations via a wireless medium.The MPDU transferred from the MAC sublayer 220 is referred to as PSDU(Physical Service Data Unit) in the PLCP sublayer 210. The MPDU issimilar to the PSDU, but in case an A-MPDU (aggregated MPDU) obtained byaggregating a plurality of MPDUs is transferred, each MPDU may bedifferent from the PSDU.

The PLCP sublayer 210 adds an additional field including necessaryinformation by a physical layer transceiver in the process of receivingthe PSDU from the MAC sublayer 220 and transferring it to the PMDsublayer 200. At this time, the added field may be a PLCP preamble inthe PSDU, a PLCP header, and tail bits necessary to get the convolutionencoder back to the zero state. The PLCP preamble plays a role to enablethe receiver to prepare for a sync function and antenna diversity beforethe PSDU is transmitted. The data fields may include padding bits in thePSDU, a service field including a bit sequence for initializing thescrambler, and a coded sequence obtained by encoding a bit sequenceadded with tail bits. At this time, as an encoding scheme, one of BCC(Binary Convolutional Coding) encoding and LDPC (Low Density ParityCheck) encoding may be selected depending on encoding schemes supportedby the STA receiving the PPDU. In the PLCP header is included a fieldcontaining information for the PPDU (PLCP Protocol Data Unit) to betransmitted, and this will be described below in more detail withreference to FIG. 3.

The PLCP sublayer 210 adds the above-described fields to the PSDU togenerate the PPDU (PLCP Protocol Data Unit) and transmits the PPDU tothe receiving station via the PMD sublayer. The receiving stationreceives the PPDU, obtains information necessary for restoring data fromthe PLCP preamble and the PLCP header, and performs restoration.

The WLAN system supports a more continuous 160 MHz band transmissionchannel and a more non-continuous 80+80 MHz band transmission channel soas to support a higher throughput. Further, it supports an MU-MIMO(Multi User-Multiple Input Multiple Output) transmission scheme. In theWLAN system supportive of the MU-MIMO transmission scheme, an AP and/oran STA to transmit data may transmit data packets to at least one ormore receiving STAs as MU-MIMO paired at the same time.

Referring back to FIG. 1, in the WLAN system illustrated in FIG. 1, AP10 may simultaneously transmit data to an STA group including at leastone or more STAs among a plurality of STAs 21, 22, 23, 24, and 30associated therewith. In FIG. 1 the AP performs MU-MIMO transmission tothe STAs, for example. However, in a WLAN system supporting TDLS(Tunneled Direct Link Setup) or DLS (Direct Link Setup) or mesh network,an STA to transmit data may transmit the PPDU to a plurality of STAsusing an MU-MIMO transmission scheme. Hereinafter, an example in whichan AP transmits the PPDU to a plurality of STAs in accordance with anMU-MIMO transmission scheme is described.

Data to be transmitted to each STA may be transmitted through spatialstreams different from each other. A data packet transmitted by AP 10 isthe PPDU or a data field included in the PPDU as generated andtransmitted from the physical layer in the WLAN system and may bereferred to as frame. That is, the data field included in the PPDU forSU-MIMO and/or MU-MIMO may be denoted MIMO packet. In an embodiment ofthe present invention, the transmission target STA group which isMU-MIMO paired with AP 10 is assumed as a group of STA1 21, STA2 22,STA3 23, and STA4 24. At this time, a specific STA in the transmissiontarget STA group may be assigned with no spatial stream and thus datatransmission may be not carried out. Meanwhile, a STAa 30 is assumed asa STA that is coupled with the AP but that is not included in thetransmission target STA group.

In the WLAN system, an identifier may be assigned to the transmissiontarget STA group to support MU-MIMO transmission, and this identifier isreferred to as group ID. The AP transmits a group ID management frameincluding group definition information for assigning the group ID toSTAs supporting MU-MIMO transmission. The group ID is assigned to theSTAs through the group ID management frame before the PPDU istransmitted. One STA may be assigned with a plurality of group IDs.

Table 1 below shows information elements included in the group IDmanagement frame:

TABLE 1 Order information 1 category 2 VHT action 3 membership status 4spatial stream position

The category field and the VHT action field are set to identify that acorresponding frame is a management frame and is a group ID managementframe used in a next-generation WLAN system supporting MU-MIMO.

As in Table 1, the group definition information includes membershipstatus information indicating whether it belongs to a specific group IDand spatial stream position information indicating a position where aspatial stream set of a corresponding STA is located in the overallspatial stream according to the MU-MIMO transmission in case it belongsto the corresponding group ID.

Since one AP manages a plurality of group IDs, the membership statusinformation provided to one STA needs to indicate whether the STAbelongs to each of the group IDs managed by the AP. Accordingly, themembership status information may be provided as an array of subfieldsindicating whether it belongs to each group ID. The spatial streamposition information indicates the position for each group ID and thusmay be presented as an array of subfields indicating the position of thespatial stream set occupied by the STA for each group ID. Further, themembership status information and the spatial stream positioninformation for one group ID may be able to be implemented in onesubfield.

In case the AP transmits the PPDU to the plurality of STAs through theMU-MIMO transmission scheme, the AP includes, as control information,information indicating the group ID in the PPDU. When the STA receivesthe PPDU, the STA verifies the group ID and identifies whether the STAis a member STA in the transmission target STA group. If it isidentified that the STA is a member of the transmission target STAgroup, the position where the spatial stream set transmitted to the STAis located in the overall spatial stream may be identified. The PPDUincludes information on the number of spatial streams assigned to thereceiving STA, and thus, the STA may receive data by figuring out thespatial streams assigned thereto.

FIG. 3 is a view illustrating an exemplary PPDU format used in a WLANsystem.

Referring to FIG. 3, a PPDU 300 may include an L-STF field 310, an L-LTFfield 320, an L-SIG field 330, a VHT-SIGA field 340, a VHT-STF field350, a VHT-LTF field 360, a VHT-SIGB field 370, and a data field 380.

A PLCP sublayer constituting a PHY adds necessary information to thePSDU transferred from the MAC layer to generate data field 380 and addsfields such as L-STF 310, L-LTF 320, L-SIG 330, VHT-SIGA field 340,VHT-STF 350, VHT-LTF 360, and VHT-SIGB 370 to generate PPDU 300. Then,the PLCP sublayer transmits PPDU 300 to one or more STAs through the PMDsublayer constituting the PHY.

L-STF 310 is used for frame timing acquisition, AGC (Automatic GainControl) convergence, and coarse frequency acquisition.

L-LTF 320 is used to estimate a channel for demodulation of L-SIG field330 and VHT-SIGA field 340.

L-SIG field 330 is used for the L-STA to receive and interpret PPDU 300to obtain data. L-SIG field 330 includes a rate subfield, a lengthsubfield, a parity bit, and a tail field. The rate subfield is set as avalue indicating a bit rate for data to be currently transmitted.

The length subfield is set as a value indicating an octet length of aPSDU requesting that the MAC layer perform transmission to the PHYlayer. At this time, a parameter related to information on the octetlength of the PSDU, L-LENGTH parameter, is determined based on a TXTIMEparameter which is a parameter related to a transmission time. TXTIMErepresents a transmission time determined by the PHY layer fortransmission of the PPDU including the PSDU corresponding to atransmission time requested by the MAC layer for transmission of thePSDU (Physical Service Data Unit). Accordingly, since the L_LENGTHparameter is related to time, the length subfield included in L-SIG 330includes information related to a transmission time.

VHT-SIGA field 340 is a field related to common control informationnecessary for STAs receiving the PPDU and includes signal information orcontrol information for interpreting the received PPDU 300. VHT-SIGAfield 340 includes channel bandwidth information used for PPDUtransmission, information indicating which one of SU or MU-MIMO is usedto transmit the PPDU, information indicating a transmission target STAgroup of a plurality of STAs MU-MIMO paired with the AP in case thetransmission scheme is MU-MIMO, information on a spatial stream assignedto each STA included in the transmission target STA group,identification information related with whether STBC (Space Time BlockCoding) is used, and information relating to a short GI (Guard Interval)of a transmission target STA.

The information indicating the MIMO transmission scheme and informationindicating the transmission target STA group may be implemented as onepiece of MIMO indicating information, for example, as a group ID. Thegroup ID may be set as a value having a specific range. In the range, aspecific value indicates an SU-MIMO transmission scheme, and the othervalues may be used as an identifier for a corresponding transmissiontarget STA group in case PPDU 300 is transmitted by the MU-MIMOtransmission scheme.

If the group ID indicates that the corresponding PPDU 300 is transmittedthrough the SU-MIMO transmission scheme, the VHT-SIGA field 340 includescoding indication information indicating whether the coding schemeapplied to the data field is BCC (Binary Convolution Coding) or LDPC(Low Density Parity Check) coding and MCS (Modulation Coding Scheme)information for a channel between a transmitter and a receiver. Further,VHT-SIGA field 340 may include AID of a transmission target STA of thePPDU and/or a partial AID including some bit sequence of the AID.

If the group ID indicates that the corresponding PPDU 300 is transmittedthrough the MU-MIMO transmission scheme, VHT-SIGA field 340 includescoding indication information indicating whether a coding scheme appliedto the data field intended to be transmitted to the MU-MIMO pairedreceiving STAs is BCC or LDPC coding. In such case, MCS (ModulationCoding Scheme) information for each STA may be included in VHT-SIGBfield 370.

VHT-STF 350 is used to enhance performance of AGC estimation whenperforming MIMO transmission.

VHT-LTF 360 is used for a STA to estimate an MIMO channel. Since thenext-generation WLAN system supports MU-MIMO, as many VHT-LTFs 360 asthe number of spatial streams over which PPDU 300 is transmitted may beset. Additionally, full channel sounding is supported, and when this isperformed, the number of VHT LTFs may be further increased.

VHT-SIGB field 370 includes dedicated control information for aplurality of MIMO paired STAs to receive PPDU 300 and obtain data.Accordingly, only when the common control information included inVHT-SIGB field 370 indicates that the currently received PPDU 300 hasbeen MU-MIMO transmitted, the STA may be designed to decode VHT-SIGBfield 370. On the contrary, in case the common control informationindicates that the currently received PPDU 300 is only for a single STA(including SU-MIMO), the STA may be designed to not decode VHT-SIGBfield 370.

VHT-SIGB field 370 includes information on the MCS (Modulation andCoding Scheme) for each STA and information on the rate matching.Further, VHT-SIGB field 370 includes information indicating the lengthof PSDU included in the data field for each STA. The informationindicating the length of the PSDU is information indicating the lengthof the bit sequence of the PSDU and may indicate the length in the unitof octet. The size of VHT-SIGB field 370 may vary depending on thechannel bandwidth used for the PPDU and the type of MIMO transmission(MU-MIMO or SU-MIMO).

Data field 380 includes data intended to be transmitted to the STA. Datafield 380 includes a service field for initializing a scrambler and aPSDU (PLCP Service Data Unit) where the MPDU (MAC Protocol Data Unit) istransmitted in the MAC layer, a tail field including a bit sequencenecessary to get the convolution encoder back to the zero state, andpadding bits for standardizing the length of the data field.

Meanwhile, to support an M2M (Machine to Machine) application, a WLANsystem attempts to back up various communication services such as smartgrid, e-health, and ubiquitous. Accordingly, sensors for sensingtemperature or moist, cameras, home appliances such as TVs, processingmachines in the factory, vehicles, and other large-scale machines mayalso be elements constituting a WLAN system supporting M2M. The M2Msupportive WLAN system has the following features:

1) large number of STAs: M2M assumes that in contrast to the existingnetwork a number of STAs are present in a BSS. This is because sensorsinstalled in homes or companies as well as devices owned by anindividual are all considered. Thus, a good number of STAs may beconnected to one AP.

2) low traffic load per STA: since an M2M terminal has a traffic patternof collecting and reporting ambient information, the information neednot be sent often and the amount thereof is small as well.

3) uplink-centered communication: M2M typically has an architecture ofreceiving a command over downlink, taking an action, and reporting dataover uplink. The main data is generally transmitted over uplink, and M2Msupportive systems stay centered on the uplink.

4) power management of STA: since an M2M terminal is primarily batterypowered and is in many cases difficult for a user to recharge often.Accordingly, a power management method is required to minimize battery'spower consumption.

5) automatic restoration function: an apparatus constituting an M2Msystem is difficult for people to manipulate in a certain circumstance,and thus, requires a self-restoring function.

Meanwhile, it is specified that an M2M supportive WLAN system is able touse a lower channel band than 6 GHz that is supported by an existingWLAN system. More specifically, it may be specified that a channel bandnot more than 1 GHz may be used. Because of using a channel band otherthan that used in the existing system, an M2M supportive WLAN system maybe relatively free in view of backward compatibility.

In the M2M supportive WLAN system, data transmission/reception of alegacy station (L-STA) may not be supported. Here, the L-STA means anSTA that transmits and receives data based on L-STF 310, L-LTF 320, andL-SIG field 330 in the PPDU 300 format. Accordingly, in case dataexchange is conducted using the PPDU format as shown in FIG. 3, amongthe types of the control information included in L-SIG field 330, thecontrol information for the L-STA only causes unnecessary overhead.

For the M2M supportive WLAN system to support MU-MIMO transmission ofthe AP and/or the STA, the control information included in a trainingfield for the MIMO channel such as VHT-SF 350 and VHT-LTF 360 of thePPDU format shown in FIG. 3, VHT-SIGA field 340, and VHT-SIGB field 370needs to be selectively included in a new PPDU format. To meet suchsystem demand, the M2M supportive WLAN system is required to provide adata transmission/reception method based on the new PPDU format. Morespecifically, the signal fields (VHT-SIGA, VHT-SIGB) included in thePPDU need to be modified.

The format of a PPDU that may be transmitted or received, according toan embodiment of the present invention, will now be described. Morespecifically, a new PPDU format is suggested by taking specific examplesof a VHT-SIGA field and a VHT-SIGB field. For ease of description, theM2M supportive WLAN system is hereinafter referred to simply as WLANsystem.

FIG. 4 shows a PPDU format that may be applicable to an embodiment ofthe present invention.

Referring to FIG. 4, a PPDU 400 includes an L-STF field 410, an L-LTFfield 420, a VHT-SIGA field 430, a VHT-STF field 440, a VHT-LTF field450, a VHT-SIGB field 460, and a data field 470.

L-STF field 410 is used for frame timing acquisition, AGC convergence,and coarse frequency acquisition. L-LTF field 420 is used to estimate achannel for decoding VHT-SIGA field 430.

VHT-STF field 440 is used to enhance performance of AGC estimation whenperforming MIMO transmission. VHT-LTF field 450 is used for an STA toestimate an MIMO channel. VHT-LTF field 450 may be set as VHT-LTF 360 ofPPDU 300 shown in FIG. 3.

Data field 470 includes a PSDU generated in the MAC layer and a PHYlayer padding bit sequence, a service field, and a tail field. InMU-MIMO transmission, data field 470 is transmitted for eachtransmission target STA and is transmitted through at least one or morespatial streams. Accordingly, data field 470 may be subjected toprecoding and beamforming before being transmitted.

A signal field including VHT-SIGA field 430 and VHT-SIGB field 460includes control information necessary for receiving STAs receiving PPDU400 from a transmitting STA to receive PPDU 400 and to demodulate anddecode data field 470, thereby obtaining the data. VHT-SIGA field 430include common control information that may be commonly applicable tothe receiving STAs, and VHT-STF field 440 includes dedicated controlinformation that may be applicable to each STA alone. Hereinafter,VHT-SIGA field 430 and VHT-SIGB field 460 are described in detail withreference to drawings.

FIG. 5 is a view illustrating a first example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 5, the VHT-SIGA field includes a BW (bandwidth) field,a short GI (guard interval) field, a VHT-length field, a group ID field,a CRC field, and a tail field.

The BW field indicates a bandwidth of a channel over which a PPDU istransmitted. The BW field may be set to indicate 20 MHz, 40 MHz, 80 MHz,160 MHz, or 80+80 MHz.

The short GI field is set to indicate whether a short GI is used.

The CRC field includes a CRC bit sequence for CRC (cyclic redundancycheck).

The tail field includes a tail bit sequence necessary to get the stateof the convolution encoder back to the zero state.

The VHT-length field may be set to include a length subfield and a ratesubfield of L-SIG field 330 in FIG. 3. A PPDU 500 shown in FIG. 5 doesnot include an L-SIG field in contrast to the existing PPDU.Accordingly, a data rate for data transmitted through the rate subfieldand the length subfield and information on the length of thecorresponding data may be included in the VHT-SIGA field and may be thentransmitted. Receiving the VHT-length field, an STA may obtaininformation relating to TXTIME through the rate subfield and the lengthsubfield.

A group ID field 514 indicates whether the corresponding PPDU ismulti-user (MU) transmitted or single user (SU) transmitted. In the caseof MU transmission, group ID field 514 includes a group ID subfieldcontaining a group ID. The group ID field further includes anumber-of-spatial streams (Nss, # of SS) subfield indicating the numberof spatial streams transmitted upon MIMO transmission.

In case the group ID in the group ID subfield is set as a specificvalue, it may be set to indicate SU transmission. For example, in casethe group ID value is 0, it may be set to indicate SU transmission. Ifthe group ID indicates SU transmission, the Nss subfield may be set toindicate the number of spatial streams transmitted to the correspondingSTA through MIMO transmission. At this time, the number of spatialstreams may be set to indicate one through up to 8.

If the group ID in the group ID subfield indicates MU transmission, theNss subfield may be set to indicate the number of spatial streamsassigned to each STA included in the transmission target STA group. Forexample, in case four STAs are included in the transmission target STAgroup, four subfields may be implemented to indicate the number ofspatial streams assigned to STA1, the number of spatial streams assignedto STA2, the number of spatial streams assigned to STA3, and the numberof spatial streams assigned to STA4, respectively. One subfield may beset to indicate a minimum of 0 to a maximum of 4 as the number ofspatial streams assigned to a specific STA.

The VHT-SIGA field may be implemented to a size of 48 bits. The BW fieldmay be set as two bits, the short GI field as one bit, the VHT-lengthfield as 16 bits, the group ID field as 19 bits, the CRC field as 4bits, and the tail field as 6 bits.

In case the PPDU is SU transmitted, the group ID subfield, the Nsssubfield, and the reserved bit sequence may be set as [4, 3, 12] bitlength or [6, 3, 10] bit length.

In case the PPDU is MU transmitted, Nss for STA1, Nss for STA2, Nss forSTA3 and Nss for STA4 subfields included in the Nss subfield, the groupID subfield, and the reserved bit sequence may be set as [4, 3, 3, 3, 3,3] or [6, 3, 3, 3, 3, 1] bit length.

Referring to FIG. 5, the VHT-SIGB field includes an MCS subfield, an FEC(forward error correction) subfield, an STBC (space time block coding)subfield, a partial AID subfield, a CRC subfield, and a tail subfield.

MCS subfield 521 is set to indicate an MCS value for a channel between atransmitting STA or an AP and a receiving STA. FEC subfield 522indicates an FEC encoding scheme applied to generate a data fieldtransmitted to the receiving STA. As an example, it may be set indicatewhether a BCC encoding scheme or an LDPC encoding scheme has been used.The STBC subfield may be set to indicate whether to apply an STBC. Thepartial AID subfield may be set as a partial AID value of a transmissiontarget STA. The partial AID subfield is a bit sequence using part of a11 bits long AID.

The VHT-SIGB field has a size of 26 bits and according to whether it isAID masked or not may be suggested as two formats. First, referring tothe left VHT-SIGB field option 1 (op1), MCS, FEC, STBC, partial AID,CRC, and tail subfield may be set in size as [4, 1, 1, 6, 8, 6] or [4,1, 1, 10, 4, 6]. Meanwhile, referring to the right VHT-SIGB field option2 (op2), MCS, FEC, STBC, partial AID, CRC, and tail subfield may be setin size as [4, 1, 1, 3, 3, 8, 6] or [4, 1, 1, 3, 7, 4, 6]. In thisexample, when doing AID masking, 11 bits constituting the partial AIDand the CRC subfield may be AID masked.

FIG. 6 is a view illustrating a second example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 6, the example is directed to a format obtained byincreasing the length of the BW field in the example shown in FIG. 5from two bits to four bits. The length of the VHT-SIGA field is fixed to48 bits, and thus, the two bits added to the BW field may be secured byreducing the length of the existing group ID field by two bits.Accordingly, the length of the group ID field turns into 17 bits. Thus,in the case of SU transmission, the group ID subfield, the Nss subfield,and the reserved bit sequence may be set in length to [4, 3, 10] bits or[6, 3, 8] bits. In contrast, in the case of MU transmission, the groupID subfield, the Nss for STA1, Nss for STA2, Nss for STA3, Nss for STA4subfields included in the Nss subfield and the reserved bit sequence maybe set in length to [4, 3, 3, 3, 3, 1] or [5, 3, 3, 3, 3, 0] bits. TheVHT-SIGB field may be the same as shown in FIG. 5.

FIG. 7 is a view illustrating a third example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 7, fields may be implemented so that the STBC subfieldis included in the VHT-SIGA field. However, assume that upon applicationof this field format STBC does not apply to MU-MIMO transmission.

Upon SU transmission, the group ID subfield, the Nss subfield, the STBCsubfield and reserved bit sequence included in the 19 bits long group IDfield may be set to [4, 3, 1, 11] bits or [6, 3, 1, 9] bits. Upon MUtransmission, the group ID field format may be set the same format asshown in FIG. 5.

In the VHT-SIGB field, as the STBC subfield is excluded, the MCSsubfield, the FEC subfield, the partial AID subfield, the CRC subfield,and the tail subfield may be set in length to [4, 1, 7, 8, 6] or [4, 1,11, 4, 6] bits (op1). Or, the MCS subfield, the FEC subfield, thereserved bit sequence, the partial AID subfield, the CRC subfield, andthe tail subfield may be set in length to [4, 1, 4, 3, 8, 6] or [4, 1,4, 7, 4, 6] (op2).

FIG. 8 is a view illustrating a fourth example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 8, the format of the group ID field in the VHT-SIGAfield is modified. In case the PPDU is MU transmitted, the Nssindication information included in the Nss subfield may be implementedto indicate an Nss field index. At this time, the Nss field index may beset as one of index values given in a table format. To be distinguishedfrom the existing Nss subfield, the Nss subfield thusly implemented isreferred to as Nss indication (number of spatial stream indication,#-of-SS indication, Nss indication) subfield. In such case, the lengthof the Nss subfield decreases from the existing 12 bits to 9 bits, andthus, the bits available in reserve increase. Refer to Table 2 below forthe table-type Nss indication information relating to the Nss indicationinformation. Meanwhile, upon SU transmission, the group ID field formatand the VHT-SIGB field format may be implemented as shown in FIG. 5.

TABLE 2 Field index SSAID#0 SSAID#1 SSAID#2 SSAID#3 0 0 0 1 1 1 0 0 1 22 0 0 1 3 3 0 0 1 4 4 0 0 2 1 5 0 0 2 2 6 0 0 2 3 7 0 0 2 4 8 0 0 3 1 90 0 3 2 10 0 0 3 3 11 0 0 3 4 12 0 0 4 1 13 0 0 4 2 14 0 0 4 3 15 0 0 44 16 0 1 0 1 17 0 1 0 2 18 0 1 0 3 19 0 1 0 4 20 0 1 1 0 21 0 1 1 1 22 01 1 2 23 0 1 1 3 24 0 1 1 4 25 0 1 2 0 26 0 1 2 1 27 0 1 2 2 28 0 1 2 329 0 1 2 4 30 0 1 3 0 31 0 1 3 1 32 0 1 3 2 33 0 1 3 3 34 0 1 3 4 35 0 14 0 36 0 1 4 1 37 0 1 4 2 38 0 1 4 3 39 0 2 0 1 40 0 2 0 2 41 0 2 0 3 420 2 0 4 43 0 2 1 0 44 0 2 1 1 45 0 2 1 2 46 0 2 1 3 47 0 2 1 4 48 0 2 20 49 0 2 2 1 50 0 2 2 2 51 0 2 2 3 52 0 2 2 4 53 0 2 3 0 54 0 2 3 1 55 02 3 2 56 0 2 3 3 57 0 2 4 0 58 0 2 4 1 59 0 2 4 2 60 0 3 0 1 61 0 3 0 262 0 3 0 3 63 0 3 0 4 64 0 3 1 0 65 0 3 1 1 66 0 3 1 2 67 0 3 1 3 68 0 31 4 69 0 3 2 0 70 0 3 2 1 71 0 3 2 2 72 0 3 2 3 73 0 3 3 0 74 0 3 3 1 750 3 3 2 76 0 3 4 0 77 0 3 4 1 78 0 4 0 1 79 0 4 0 2 80 0 4 0 3 81 0 4 04 82 0 4 1 0 83 0 4 1 1 84 0 4 1 2 85 0 4 1 3 86 0 4 2 0 87 0 4 2 1 88 04 2 2 89 0 4 3 0 90 0 4 3 1 91 0 4 4 0 92 1 0 0 1 93 1 0 0 2 94 1 0 0 395 1 0 0 4 96 1 0 1 0 97 1 0 1 1 98 1 0 1 2 99 1 0 1 3 100 1 0 1 4 101 10 2 0 102 1 0 2 1 103 1 0 2 2 104 1 0 2 3 105 1 0 2 4 106 1 0 3 0 107 10 3 1 108 1 0 3 2 109 1 0 3 3 110 1 0 3 4 111 1 0 4 0 112 1 0 4 1 113 10 4 2 114 1 0 4 3 115 1 1 0 0 116 1 1 0 1 117 1 1 0 2 118 1 1 0 3 119 11 0 4 120 1 1 1 0 121 1 1 1 1 122 1 1 1 2 123 1 1 1 3 124 1 1 1 4 125 11 2 0 126 1 1 2 1 127 1 1 2 2 128 1 1 2 3 129 1 1 2 4 130 1 1 3 0 131 11 3 1 132 1 1 3 2 133 1 1 3 3 134 1 1 4 0 135 1 1 4 1 136 1 1 4 2 137 12 0 0 138 1 2 0 1 139 1 2 0 2 140 1 2 0 3 141 1 2 0 4 142 1 2 1 0 143 12 1 1 144 1 2 1 2 145 1 2 1 3 146 1 2 1 4 147 1 2 2 0 148 1 2 2 1 149 12 2 2 150 1 2 2 3 151 1 2 3 0 152 1 2 3 1 153 1 2 3 2 154 1 2 4 0 155 12 4 1 156 1 3 0 0 157 1 3 0 1 158 1 3 0 2 159 1 3 0 3 160 1 3 0 4 161 13 1 0 162 1 3 1 1 163 1 3 1 2 164 1 3 1 3 165 1 3 2 0 166 1 3 2 1 167 13 2 2 168 1 3 3 0 169 1 3 3 1 170 1 3 4 0 171 1 4 0 0 172 1 4 0 1 173 14 0 2 174 1 4 0 3 175 1 4 1 0 176 1 4 1 1 177 1 4 1 2 178 1 4 2 0 179 14 2 1 180 1 4 3 0 181 2 0 0 1 182 2 0 0 2 183 2 0 0 3 184 2 0 0 4 185 20 1 0 186 2 0 1 1 187 2 0 1 2 188 2 0 1 3 189 2 0 1 4 190 2 0 2 0 191 20 2 1 192 2 0 2 2 193 2 0 2 3 194 2 0 2 4 195 2 0 3 0 196 2 0 3 1 197 20 3 2 198 2 0 3 3 199 2 0 4 0 200 2 0 4 1 201 2 0 4 2 202 2 1 0 0 203 21 0 1 204 2 1 0 2 205 2 1 0 3 206 2 1 0 4 207 2 1 1 0 208 2 1 1 1 209 21 1 2 210 2 1 1 3 211 2 1 1 4 212 2 1 2 0 213 2 1 2 1 214 2 1 2 2 215 21 2 3 216 2 1 3 0 217 2 1 3 1 218 2 1 3 2 219 2 1 4 0 220 2 1 4 1 221 22 0 0 222 2 2 0 1 223 2 2 0 2 224 2 2 0 3 225 2 2 0 4 226 2 2 1 0 227 22 1 1 228 2 2 1 2 229 2 2 1 3 230 2 2 2 0 231 2 2 2 1 232 2 2 2 2 233 22 3 0 234 2 2 3 1 235 2 2 4 0 236 2 3 0 0 237 2 3 0 1 238 2 3 0 2 239 23 0 3 240 2 3 1 0 241 2 3 1 1 242 2 3 1 2 243 2 3 2 0 244 2 3 2 1 245 23 3 0 246 2 4 0 0 247 2 4 0 1 248 2 4 0 2 249 2 4 1 0 250 2 4 1 1 251 24 2 0 252 3 0 0 1 253 3 0 0 2 254 3 0 0 3 255 3 0 0 4 256 3 0 1 0 257 30 1 1 258 3 0 1 2 259 3 0 1 3 260 3 0 1 4 261 3 0 2 0 262 3 0 2 1 263 30 2 2 264 3 0 2 3 265 3 0 3 0 266 3 0 3 1 267 3 0 3 2 268 3 0 4 0 269 30 4 1 270 3 1 0 0 271 3 1 0 1 272 3 1 0 2 273 3 1 0 3 274 3 1 0 4 275 31 1 0 276 3 1 1 1 277 3 1 1 2 278 3 1 1 3 279 3 1 2 0 280 3 1 2 1 281 31 2 2 282 3 1 3 0 283 3 1 3 1 284 3 1 4 0 285 3 2 0 0 286 3 2 0 1 287 32 0 2 288 3 2 0 3 289 3 2 1 0 290 3 2 1 1 291 3 2 1 2 292 3 2 2 0 293 32 2 1 294 3 2 3 0 295 3 3 0 0 296 3 3 0 1 297 3 3 0 2 298 3 3 1 0 299 33 1 1 300 3 3 2 0 301 3 4 0 0 302 3 4 0 1 303 3 4 1 0 304 4 0 0 1 305 40 0 2 306 4 0 0 3 307 4 0 0 4 308 4 0 1 0 309 4 0 1 1 310 4 0 1 2 311 40 1 3 312 4 0 2 0 313 4 0 2 1 314 4 0 2 2 315 4 0 3 0 316 4 0 3 1 317 40 4 0 318 4 1 0 0 319 4 1 0 1 320 4 1 0 2 321 4 1 0 3 322 4 1 1 0 323 41 1 1 324 4 1 1 2 325 4 1 2 0 326 4 1 2 1 327 4 1 3 0 328 4 2 0 0 329 42 0 1 330 4 2 0 2 331 4 2 1 0 332 4 2 1 1 333 4 2 2 0 334 4 3 0 0 335 43 0 1 336 4 3 1 0 337 4 4 0 0

FIG. 9 is a view illustrating a fifth example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 9, the signal field format corresponds to a formatobtained by expanding the length of the BW field from two bits to fourbits. The length of the VHT-SIGA field is fixed to 48 bits, and thus,the two bits added to the BW field may be secured by reducing the lengthof the group ID field by two bits. Accordingly, the length of the groupID field is reduced from 19 bits to 17 bits. In the case of SUtransmission, the group ID subfield, the Nss subfield, and the reservedbit sequence may be set in length to [4, 3, 10] or [6, 3, 8] bits. Onthe contrary, in the case of MU transmission, the group ID subfield, theNss indication subfield, and the reserved bit sequence may be set inlength to [4, 9, 4] or [6, 9, 2] bits. The specific format of theVHT-SIGB field is shown in FIG. 5.

FIG. 10 is a view illustrating a sixth example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 10, the signal field may be set so that the STBCsubfield included in the VHT-SIGB field is included in the VHT-SIGAfield. However, assume, in this example, that in case the PPDU includingthe signal filed is MU transmitted, the STBC does not apply. In thegroup ID field having a length of 19 bits, upon SU transmission, thegroup ID subfield, the Nss subfield, the STBC subfield, and the reservedbit sequence may be set in length to [4, 3, 1, 11] or [6, 3, 1, 9] bits.Meanwhile, in the case of MU transmission, the group ID subfield, theNss indication subfield, and the reserved bit sequence may be set inlength to [4, 9, 6] or [6, 9, 4] bits.

Since the VHT-SIGB field has the STBC subfield excluded, the MCSsubfield, the FEC subfield, the partial AID subfield, the CRC subfield,and the tail subfield may be set in length to [4, 1, 7, 8, 6] bits or[4, 1, 11, 4, 6] bits (op1). Or, 4 bits in the partial AID subfield maybe set as a reserved bit sequence (op2). Accordingly, the MCS subfield,the FEC subfield, the reserved bit sequence, the partial AID subfield,the CRC subfield, and the tail subfield may be set in length to [4, 1,4, 3, 8, 6] bits or [4, 1, 4, 7, 4, 6] bits.

FIG. 11 is a view illustrating a seventh example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 11, the signal field has a format in which the lengthof the CRC field in the VHT-SIGA field has been increased to 8 bits inthe signal field format as shown in FIG. 8. Accordingly, the length ofthe group ID field in the VHT-SIGA field is set to 15 bits. In the groupID field, upon SU transmission, the group ID subfield, the Nss subfield,and the reserved bit sequence may be [4, 3, 8] bits long or [6, 3, 6]bits long. Meanwhile, upon MU transmission, the group ID subfield, theNss indication subfield, and the reserved bit sequence may be set inlength to [4, 9, 2] or [6, 9, 0] bits. The format of the VHT-SIGB fieldmay be set to be the same as the format shown in FIG. 8.

FIG. 12 is a view illustrating an eighth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 12, the length of the VHT-SIGA field is increased fromtwo bits to four bits, and the length of the CRC field is increased to 8bits. In this example, the increased bits in the BW field and in the CRCfield may be ones assigned instead of the bits that are conventionallyassigned to the group ID field. Accordingly, the length of the group IDfield turns into 13 bits.

Upon SU transmission, in the group ID field, the group ID subfield, theNss subfield, and the reserved bit sequence may be set in length to [4,3, 6] bits. In contrast, upon MU transmission, the group ID subfield andthe Nss indication subfield may be set in length to [4, 9] bits. Theformat of the VHT-SIGB field may be set to be the same as the formatshown in FIG. 8.

FIG. 13 is a view illustrating a ninth example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 13, the format of the VHT-SIGA field is set to be thesame as the format shown in FIG. 5. In contrast, the VHT-SIGB field isset to be different from the existing field format. However, unlike theexisting one, the length of the VHT-SIGB field may be implemented as 24bits.

In the VHT-SIGB field of op1 where AID masking does not apply, the MCSsubfield, the FEC subfield, the STBC subfield, the partial AID subfield,the CRC subfield, and the tail subfield may be set in length to [4, 1,1, 4, 8, 6] or [4, 1, 1, 8, 4, 6]. The AID is a 11 bits long bitsequence. Here, the partial AID means a bit sequence using part of atotal of 11 bits.

Meanwhile, in the VHT-SIGB field of op2 where AID masking applies, theMCS subfield, the FEC subfield, the STBC subfield, the reserved bitsequence, the partial AID subfield, the CRC subfield, and the tailsubfield may be set in length to [4, 1, 1, 1, 3, 8, 6] or [4, 1, 1, 1,7, 4, 6]. The 11-bit bit sequence constituting the partial AID subfieldand the CRC subfield may be implemented to be AID masked.

FIG. 14 is a view illustrating a tenth example of a signal field formataccording to an embodiment of the present invention.

Referring to FIG. 14, this signal field format corresponds to a formatobtained by expanding the length of the BW field from two bits to fourbits in the signal field format shown in FIG. 13. Since the length ofthe VHT-SIGA field is fixed to 48 bits, the two bits added to the BWfield may be secured by reducing the length of the group ID field by twobits. Accordingly, the length of the group ID field is reduced from 19bits to 17 bits. In the case of SU transmission, the group ID subfield,the Nss subfield, and the reserved bit sequence may be set in length to[4, 3, 10] or [6, 3, 8] bits. In contrast, in the case of MUtransmission, the group ID subfield, the Nss indication subfield, andthe reserved bit sequence may be set in length to [4, 9, 4] or [6, 9, 2]bits. A specific format of the VHT-SIGB field is the same as the formatshown in FIG. 13.

FIG. 15 is a view illustrating an eleventh example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 15, the signal field may be set so that the STBCsubfield included in the VHT-SIGB field may be included in the VHT-SIGAfield. However, assume, in this example, that in case the PPDU includingthe signal field is MU transmitted, the STBC does not apply. In thegroup ID field having a length of 19 bits, upon SU transmission, thegroup ID subfield, the Nss subfield, the STBC subfield, and the reservedbit sequence may be set in length to [4, 3, 1, 11] or [6, 3, 1, 9] bits.Meanwhile, upon MU transmission, the group ID subfield, the Nss forSTA1, Nss for STA2, Nss for STA3, and Nss for STA4 subfieldsconstituting the Nss subfield, and the reserved bit sequence may be setin length to [4, 3, 3, 3, 3, 3] or [6, 3, 3, 3, 3, 1] bits.

Since the VHT-SIGB field has the STBC subfield excluded, the MCSsubfield, the FEC subfield, the partial AID subfield, the CRC subfield,and the tail subfield may be set in length to [4, 1, 5, 8, 6] or [4, 1,9, 4, 6] bits (op1). Or, two bits in the partial AID subfield may be setas a reserved bit sequence (op2). That is, in op2 where AID maskingapplies, the MCS subfield, the FEC subfield, the reserved bit sequence,the partial AID subfield, the CRC subfield, and the tail subfield may beset in length to [4, 1, 2, 3, 8, 6] or [4, 1, 2, 7, 4, 6] bits.

FIG. 16 is a view illustrating a twelfth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 16, the length of the CRC field in the VHT-SIGA fieldis increased to 8 bits. Accordingly, the length of the VHT-SIGA field isreduced from 19 bits to 15 bits. In the group ID field, upon SUtransmission, the group ID subfield, the Nss subfield, the STBCsubfield, and the reserved bit sequence may be set in length to [4, 3,1, 7] or [6, 3, 1, 5] bits. Meanwhile, upon MU transmission, the groupID subfield, the Nss indication subfield, and the reserved bit sequencemay be set in length to [4, 9, 2] or [6, 9, 0] bits. The VHT-SIGB fieldmay be set to be the same as shown in FIG. 15.

FIG. 17 is a view illustrating a thirteenth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 17, in the format shown in FIG. 13, the length of theBW field is increased from two bits to four bits, and the length of theCRC field in the VHT-SIGA field is increased to 8 bits. The increasedbits in the BW field and the CRC field may be implemented by insteadassigning bits that conventionally constitute the group ID field.Accordingly, the length of the group ID field is set as 13 bits.

In the group ID field, upon SU transmission, the group ID subfield, theNss subfield, and the reserved bit sequence may be set in length to [4,3, 6] bits. Meanwhile, upon MU transmission, the group ID subfield andthe Nss indication subfield may be set in length to [4, 9] bits. TheVHT-SIGB field may be set to be the same as shown in FIG. 14.

FIG. 18 is a view illustrating a fourteenth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 18, in the signal field shown in FIG. 8, upon SUtransmission and upon MU transmission, the group ID field format is setto be the same. In the group ID field, the group ID subfield, the Nssindication subfield, and the reserved bit sequence may be set in lengthto [4, 9, 6] or [6, 9, 4] bits. Other fields constituting the VHT-SIGAfield and the VHT-SIGB field have the same format as the format shown inFIG. 8.

FIG. 19 is a view illustrating a fifteenth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 19, in the signal field shown in FIG. 18, the lengthof the BW field is increased from two bits to four bits. Since thelength of the VHT-SIGA field is fixed to 48 bits, two bits included inthe existing group ID field may be assigned as the increased two bits inthe BW field. Accordingly, the length of the group ID field is reducedto 17 bits. In the group ID field, the group ID subfield, the Nssindication subfield, and the reserved bit sequence may be set in lengthto [4, 9, 4] or [6, 9, 2] bits. Other fields constituting the VHT-SIGAfield and the VHT-SIGB field have the same format as the format shown inFIG. 18.

FIG. 20 is a view illustrating a sixteenth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 20, in the signal field shown in FIG. 18, the lengthof the CRC field in the VHT-SIGA field is increased to 8 bits.Accordingly, the length of the group ID field is reduced to 15 bits. Inthe group ID field, the group ID subfield, the Nss indication subfield,and the reserved bit sequence may be set in length to [4, 9, 2] or [6,9, 0] bits. Other fields constituting the VHT-SIGA field and theVHT-SIGB field have the same format as the format shown in FIG. 18.

FIG. 21 is a view illustrating a seventeenth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 21, in the signal field shown in FIG. 18, the lengthof the BW field in the VHT-SIGA field is increased to four bits, and thelength of the CRC field is increased to 8 bits. The increased bits inthe BW field and the CRC field may be set to use existing bitsconstituting the group ID field. Accordingly, the length of the group IDfield is 13 bits. In the group ID field, the group ID subfield, the Nssindication subfield, and the reserved bit sequence may be set in lengthto [4, 9, 0] bits. Other fields in the VHT-SIGA field and the VHT-SIGBfield have the same format as the format shown in FIG. 18.

In the signal field shown in FIGS. 5 to 21, the VHT-SIGB field may beset to further include a VHT-length 2 field independent from theVHT-length field of the VHT-SIGA field. In such case, the VHT-length 2field may be set to indicate the length for the data field 470constituting the PPDU 400, the PSDU included in the data field 470,and/or valid data constituting the PSDU. The length may be representedas the number of OFDM symbols, time unit (e.g., μs), payload size, octetunit, or bit unit, etc.

In FIGS. 5 to 21, the format of a specific VHT-SIGA field and the formatof a specific VHT-SIGB field may be organically combined with each otherand are thus set to include control information intended to betransmitted to a receiving STA. However, the above-described individualVHT-SIGA field and the VHT-SIGB field format may also be implemented tobe independently included in the PPDU. Accordingly, among the signalfield formats suggested above, the VHT-SIGA field and the VHT-SIGB fieldincluded in the examples different from each other may be mixed witheach other, thus suggesting a new signal field format.

FIG. 22 is a view illustrating an eighteenth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 22, the signal field in this example is a formatobtained by deleting the VHT-length field from the signal field shown inFIG. 5, removing the VHT-SIGB field, and incorporating it into theVHT-SIGA field. The VHT-SIGA field includes a BW field, a short GIfield, an STBC field, an FEC field, a group ID field, a CRC field, and atail field. The length of the VHT-SIGA field may be fixed to 48 bits.

The BW field, the short GI field, the STBC field, the FEC field, thegroup ID field, the reserved bit sequence, the CRC field, and the tailfield may be set in length to [2, 1, 1, x, 33-x, 4, 6] bits. The groupID field assigned with x bits includes a group ID subfield, an Nssindication subfield, and an MCS subfield. Refer to the drawings for thespecific format of each subfield constituting the group ID field.

FIG. 23 is a view illustrating a nineteenth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 23, the signal field in this example has a format inwhich the length of the BW subfield has been increased by two bits.Accordingly, the length of the reserved bit sequence may be determinedas 31-x bits.

FIG. 24 is a view illustrating a twentieth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 24, the signal field in this example has a format inwhich the length of the CRC field has been increased from four bits toeight bits. Accordingly, the length of the reserved bit sequence may bedetermined as 29-x bits.

FIG. 25 is a view illustrating a twenty-first example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 25, the signal field in this example has a format inwhich the length of the STBC field has been increased to four bits. Theexisting STBC field has a length of one bit and indicates whether STBCapplies according to the value of the corresponding field. In contrast,the STBC field set to a length of four bits may be rendered to be ableto indicate whether the STBC applies to each STA included in thetransmission target STA group. If the MU-MIMO transmission scheme maysupport more transmission target STAs, the length of the STBC field maybe further increased. Accordingly, the length of the reserved bitsequence may be determined as 30-x bits.

FIG. 26 is a view illustrating a twenty-second example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 26, the signal field in this example has a format inwhich the length of the FEC field has been increased to four bits. Inthe signal field shown in FIG. 22, the FEC field has a length of one bitand indicates whether BCC encoding or LPDC encoding has appliedaccording to a set value. In contrast, the 4 bits long FEC field isrendered to be able to indicate an encoding scheme that has applied toeach STA included in the transmission target STA group. Accordingly, thelength of the reserved bit sequence may be determined as 30-x bits.

FIG. 27 is a view illustrating a twenty-third example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 27, the signal field in this example has a format inwhich the length of the BW field is set to four bits and the length ofthe CRC field is set to 8 bits. Accordingly, the length of the reservedbit sequence is determined as 27-x bits.

FIG. 28 is a view illustrating a twenty-fourth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 28, the signal field in this example has a format inwhich the STBC field and the FEC field each are set in length to 4 bits.Accordingly, the length of the reserved bit sequence is determined as27-x bits.

FIG. 29 is a view illustrating a twenty-fifth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 29, the signal field in this example has a format inwhich the BW field and the STBC field each are set in length to fourbits. Accordingly, the length of the reserved bit sequence is determinedas 28-x bits.

FIG. 30 is a view illustrating a twenty-sixth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 30, the signal field in this example has a format inwhich the BW field and the FEC field each are set in length to fourbits. Accordingly, the length of the reserved bit sequence is determinedas 28-x bits.

FIG. 31 is a view illustrating a twenty-seventh example of a signalfield format according to an embodiment of the present invention.

Referring to FIG. 31, the signal field in this example has a format inwhich the STBC field and the CRC field respectively are set in length tofour bits and eight bits. Accordingly, the length of the reserved bitsequence is determined as 26-x bits.

FIG. 32 is a view illustrating a twenty-eighth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 32, the signal field in this example has a format inwhich the FEC field and the CRC field respectively are set in length tofour bits and eight bits. Accordingly, the length of the reserved bitsequence is determined as 26-x bits.

Referring to FIGS. 22 to 32, the group ID field of the signal field mayhave various formats. The group ID subfield included in the group IDfield includes a group ID indicating a transmission target STA group.The group ID subfield may have a length of 4 bits or 6 bits.

The Nss indication subfield indicates the number of spatial streamsassigned to each STA included in the transmission target STA group. TheNss indication subfield may be implemented to have a format including aplurality of subfields indicating the number of spatial streams assignedto each STA. Further, the Nss indication subfield may be implemented tobe set to have an index value as exemplified in Table 2. However, incase the length of the Nss indication subfield is 12 bits or more, theNss indication subfield may be implemented in one of the above-describedtwo types. In contrast, in case the length is less than 12 bits, the Nssindication subfield is set to have an index value.

The group ID field further includes an MCS subfield. The MCS subfieldindicates MCS information on a specific STA. The MCS subfield mayinclude a plurality of subfields to indicate an MCS for each STA. As anexample, in case four STAs are included in the transmission target STAgroup, the MCS subfield may include MCS for STA1, MCS for STA2, MCS forSTA3 and MCS for STA4.

FIG. 33 is a view illustrating a twenty-ninth example of a signal fieldformat according to an embodiment of the present invention.

Referring to FIG. 33, a signal field format is suggested to define theVHT-length field by dividing it into a VHT-SIGA field and a VHT-SIGBfield. The VHT-SIGA field includes a BW field, a short GI field, an STBCfield, a group ID field, an Nss field, a VHT-length 1 field, a CRCfield, and a tail field. The VHT-length 1 field may be set to be x bitslong. The VHT-SIGB field includes an MCS field, an FEC field, aVHT-length 2 field, a CRC field, and a tail field. The VHT-length 2field may be set to be y bits long. The remaining fields except for theVHT-length 1 and 2 fields may be set to be the same as the correspondingfields in the existing drawings. A method of interpreting the VHT-length1 field and the VHT-length 2 field is now described below in detail.

1) a bit sequence constituting the VHT-length 1 field and a bit sequenceconstituting the VHT-length 2 field may be combined and may beinterpreted as a single VHT-length field. That is, a value indicated bythe bit sequence is interpreted as a packet length. The packet lengthmay be represented as the number of OFDM symbols, time unit (e.g., μs),or payload size. An example is described with reference to FIG. 34.

FIG. 34 is a view illustrating an example of implementing lengthindication information that may be applicable to an embodiment of thepresent invention.

Referring to FIG. 34, assume that the five bits long VHT-length 1 fieldis set as [0, 1, 1, 0, 1], and the seven bits long VHT-length 2 field isset as [1, 0, 1, 0, 1, 0, 1]. In such case, when the receiving STAreceives of the VHT-length 1 field and the VHT-length 2 field, the bitsequence as information indicating the length may be interpreted as [0,1, 1, 0, 1, 1, 0, 1, 0, 1, 0, 1]. Accordingly, it can be seen that thelength of the data field has a value corresponding to a binary number011011010101₂.

2) the length of the data field may be interpreted as being indicated byadjusting to a VHT-length 2 field value with respect to a VHT-length 1field. The VHT-length 1 field is transmitted while being included in theVHT-SIGA field, and thus, may be received by all of the STAs in thetransmission target STA group. The VHT-length 2 field is transmittedwhile being included in the VHT-SIGB field, and thus, may be set toindicate a different value to each STA. Accordingly, it is useful toindicate the length of the data field transmitted to each STA uponMU-MIMO transmission. However, a value indicated by a combination of theVHT-length 1 afield and the VHT-length 2 field may be represented as thenumber of OFDM symbols, time unit (e.g., μs), or payload size. Anexample is described in connection with FIG. 35.

FIG. 35 is a view illustrating another example of implementing lengthindication information that may be applicable to an embodiment of thepresent invention.

Referring to FIG. 35, assume that the seven bits long VHT-length 1 fieldis set as [0, 1, 1, 0, 1, 1, 1] and the three bits long VHT-length 2field is set as [1, 0, 1] for STA1 and as [0, 1, 0] for STA2. STA1 andSTA2 are MU-MIMO paired STAs and are included in the transmission targetSTA group.

The length of the data field transmitted to each STA may be interpretedas 101₂/010₂ with respect to 0110111₂. At this time, the VHT-length 2field value may be implemented as being + operated or − operated. Incase the value is set as being + operated, the data field for STA1 has alength of 0110111₂+101₂ and the data field for STA2 has a length of0110111₂+010₂010₂.

The signal field applicable to an embodiment of the present invention assuggested with reference to FIGS. 5 to 21 is an example of including aVHT-SIGA field and a VHT-SIGB field. At this time, the FEC subfieldindicating an encoding scheme as applied is included in the VHT-SIGBfield. It is because supportable encoding/decoding scheme may changedepending on capability of the receiving STA. In case the FEC field isincluded in the VHT-SIGB field, the AP and/or transmitting STA mayindicate an encoding scheme applied by naturally setting an FEC subfieldvalue to fit the capability of the receiving STA. In a method ofindicating the encoding scheme, if the FEC subfield value is 0, BCCencoding may be indicated, and if the FEC subfield value is 1, LDPCencoding may be indicated, and vice versa.

For example, assume that the MU-MIMO-based transmission target STA groupincludes STA1, STA2, STA3, and STA4. Although STA1 and STA2 support bothBCC encoding and LDPC encoding schemes, STA3 and STA4 may support BCCencoding scheme alone. In such case, the FEC subfield of the VHT-SIGBfield intended to be transmitted to STA1 and STA2 may be set to indicateone of the BCC encoding and LDPC encoding schemes, and the FEC subfieldof the VHT-SIGB field intended to be transmitted to STA3 and STA4 is setto indicate the BCC encoding scheme. Receiving the VHT-SIGB field, theSTA may detect/decode data according to BCC or LDPC scheme based on theFEC subfield value.

Meanwhile, latency may occur when the FEC subfield is included in theVHT-SIGB field. That is, this is why decoding data may not be initiatedbefore the FEC subfield value in the VHT-SIGB field is known. To addressthis, the FEC subfield may be included in the VHT-SIGA field.

To support MU-MIMO, as much length indication information as the numberof MU-MIMO transmission target STAs should be included in the VHT-SIGAfield. Due to this, unless a sufficient space is provided in theVHT-SIGA field, a one bit long FEC subfield may be included in theVHT-SIGA field. In such case, it is suggested how to support MU-MIMO ofSTAs having various capability values.

The one bit long FEC subfield may back up the following three instances.Assume that among STAs, an STA supporting LDPC encoding may support BCCencoding as well. The FEC subfield being 0 means the BCC schemes, andthe FEC subfield being 1 means the LDPC scheme.

Case 1: In Case all STAs in the Group Supports BCC Encoding Only

Assume that the AP transmits data to STA1, STA2, STA3, and STA4 throughMU-MIMO. At this time, all the STAs have BCC capability values. Atransmitter transmits the FEC subfield of the VHT-SIGA field with theFEC subfield set as 0. Transmission target STAs, i.e., STA1, STA2, STA3,and STA4, all decode the data corresponding to the BCC encoding scheme.

Case 2: In Case all STAs in the Group Support LDPC Encoding

Assume that the AP transmits data to STA1, STA2, STA3, and STA4 throughMU-MIMO. At this time, all the STAs have LDPC capability values. The APtransmits the FEC subfield of the VHT-SIGA field with the FEC subfieldset as 1. Transmit target STAs, i.e., STA1, STA2, STA3, and STA4, alldecode the data corresponding to the LDPC encoding scheme.

Case 3: In Case Some of all STAs in the Group Support LDPC Encoding

Assume that the AP transmits data to STA1, STA2, STA3, and STA4 throughMU-MIMO. At this time, some STAs have LDPC capability values. Forexample, STA1 and STA2 have LDPC capability values. At this time, the APtransmits the FEC field of the VHT-SIGA field with the FEC field setas 1. STA1 and STA2 support LDPC encoding and thus decode the datacorresponding to LDPC encoding. In the case of STA3 and STA4, althoughthe FEC subfield value means LDPC encoding, their capability valuessupport BCC encoding only, and thus, the FEC subfield value isdisregarded. In other words, an STA, when information indicating acoding scheme not supportable by the STA is included in the VHT-SIGAfield, disregards the value and decodes data corresponding to a codingscheme supportable by its capability value.

To support the above schemes, the formats of the VHT-SIGA field and theVHT-SIGB field as suggested in FIGS. 5 to 21 should be modified. Thatis, the FEC subfield is included in the VHT-SIGA field, and the lengthof the reserved bit sequence is reduced. Further, the FEC subfield isexcluded from the VHT-SIGB field, and the length of the partial AIDsubfield or reserved bit sequence is increased. Similarly, like theformats shown in FIGS. 22 to 25, 27, 29, and 31, the signal field isimplemented with only the VHT-SIGA field without the VHT-SIGB field, andthe length of the FEC field is likewise specified as one bit. With theone bit long FEC subfield as suggested above, MU-MIMO may be supportedin a system constituted of heterogeneous devices.

FIG. 36 is a view illustrating an example of a Tx procedure based on aPPDU format according to an embodiment of the present invention.

Referring to FIG. 36, an MAC layer transfers a generated MPDU or A-MPDUto a PLCP sublayer. In the PLCP sublayer, the MPDU or A-MPDU is referredto as PSDU. The PLCP sublayer transmits the PSDU to another STA througha PHY layer and adds necessary control information for the other STA toreceive, demodulate, and decode a corresponding PPDU to thereby obtainthe data. The corresponding control information may be included in theVHT-SIGA field and the VHT-SIGB field. A type-of-encoder (in case of BCCencoder) tail field may be added. The control information may beincluded in the VHT-SIGA field and the VHT-SIGB field. Although notshown, in case only the VHT-SIGA field is implemented as the signalfield, the corresponding control information is included in the VHT-SIGAfield. Refer to FIGS. 5 to 33 for the formats of the VHT-SIGA field andthe VHT-SIGB field.

The PLCP sublayer may add training symbols for antenna diversityacquisition, and timing acquisition and wireless resourcesynchronization between a transmitting AP and/or STA and a receivingSTA. This may be implemented by adding VHT training symbols including aVHT-STF and a VHT-LTF necessary for demodulating and decoding the datafield and the VHT-SIGB field transmitted through an MIMO channel andlegacy training symbols including the L-STF and L-LTF necessary fordemodulating and decoding the VHT-SIGA field.

The PPDU transmitted through a wireless resource is mapped with an OFDMsymbol and is transmitted through a wireless resource. Here, the PPDUand/or the data field in the PPDU mapped with the OFDM symbol may beimplemented to have a specific bit size and may be implemented to have abit size of a multiple of the above-described Octet. Accordingly, incase the bit size is not enough to supplement the bit size of the PPDUand/or data field, a padding bit may be added to adjust the overall bitsize of the PPDU and/or data field.

The PPDU generated in Tx procedure includes a preamble for STA, a signalfield (VHT-SIGA and/or VHT-SIGB) including control information, aservice field, a PSDU, a tail field, and a data field including thepadding field. The generated PPDU is mapped with an OFDM symbol and maybe transmitted to at least one or more destination STAs MIMO paired witheach other.

FIG. 37 is a view illustrating an example of an Rx procedure for a PPDUgenerated according to an embodiment of the present invention.

Referring to FIG. 37, the receiving STA obtains timing synchronizationand channel information based on the L-preamble and VHT-preamble andobtains control information included in the signal field. The STAdemodulates and decodes the data field diagnosis through each spatialstream based on the control information and transmits the PSDU to theMAC layer.

FIG. 38 is a block diagram illustrating a wireless device to which anembodiment of the present invention may be applicable. The wirelessdevices may be an AP or an STA.

A wireless device 1000 includes a processor 1010, a memory 1020, and atransceiver 1030. Transceiver 1030 transmits/receives a wireless signal.An IEEE 802.11 based physical layer is implemented in transceiver 1030.Processor 1010 is functionally coupled with the transceiver 1030 andimplements an IEEE 802.11 MAC layer and physical layer. Processor 1010may be configured to generate a PPDU format as suggested herein andconfigured to transmit the PPDU format. Processor 1010 may also beconfigured to receive the transmitted PPDU, configured to interpretfield values therein to obtain control information, and configured toobtain data using the control information. The processor may beconfigured to implement the embodiments of the present inventiondescribed above in connection with FIGS. 2 to 37.

Processor 1010 and/or transceiver 1030 may include ASICs(application-specific integrated circuits), other chipsets, logicalcircuits and/or data processing devices. Memory 1020 may include a ROM(read-only memory), a RAM (random access memory), a flash memory, amemory card, a storage medium and/or other storage devices. When theembodiments are implemented in software, the above-described schemes maybe embodied in modules (procedures or functions). The modules may bestored in memory 1020 and may be executed by processor 1010. Memory 1020may be positioned in or outside processor 1010 and may be connected toprocessor 1010 through various known means.

The embodiments described above are merely provided as examples tointroduce the technical spirit of the present invention, and thetechnical spirit of the present invention should not be limited thereto.The scope of the present invention is defined by the appended claims.

1. A method for receiving data in a wireless local area network, themethod comprising: determining a type of a physical layer protocol dataunit (PPDU); and receiving the PPDU according to the determined type ofthe PPDU, wherein the type of the PPDU is determined as a single user(SU)-type PPDU destined to a single receiver or a multi user (MU)-typePPDU destined to a plurality of receivers, the SU-type PPDU includes afirst short training field (STF), a first long training field (LTF), alegacy-signal field (L-SIG), a signal-A field, a second STF, a secondLTF and an SU data portion; and the MU-type PPDU includes a first STF, afirst LTF, a L-SIG, a signal-A field, a signal-B field, a second STF, asecond LTF and an MU data portion.
 2. The method of claim 1, wherein thesignal-A field of the SU-type PPDU and the signal-A field of the MU-typePPDU respectively include bandwidth information indicating a bandwidthin which a corresponding PPDU is transmitted.
 3. The method of claim 1,wherein the signal-A field of the SU-type PPDU includes a modulation andcoding scheme (MCS) for the SU data portion and the signal-B field ofthe MU-type PPDU includes a MCS for the MU data portion.
 4. The methodof claim 1, wherein the signal-B field of the MU-type PPDU includespartial association identifiers (AIDs) identifying the plurality ofreceivers.
 5. The method of claim 1, wherein the signal-A field of theSU-type PPDU includes information on a number of spatial streamsassigned to the receiver and the signal-B field of the MU-type PPDUincludes information on a number of spatial streams assigned to theplurality of receivers.
 6. A device for a wireless local area network,the device comprising: a transceiver configured to transmit radiosignals; and a processor operatively coupled with the transceiver andconfigured to: determine a type of a physical layer protocol data unit(PPDU); and control the transceiver to receive the PPDU according to thedetermined type of the PPDU, wherein the type of the PPDU is determinedas a single user (SU)-type PPDU destined to a single receiver or a multiuser (MU)-type PPDU destined to a plurality of receivers, the SU-typePPDU includes a first short training field (STF), a first long trainingfield (LTF), a legacy-signal field (L-SIG), a signal-A field, a secondSTF, a second LTF and an SU data portion; and the MU-type PPDU includesa first STF, a first LTF, a L-SIG, a signal-A field, a signal-B field, asecond STF, a second LTF and an MU data portion.
 7. The device of claim6, wherein the signal-A field of the SU-type PPDU and the signal-A fieldof the MU-type PPDU respectively include bandwidth informationindicating a bandwidth in which a corresponding PPDU is transmitted. 8.The device of claim 6, wherein the signal-A field of the SU-type PPDUincludes a modulation and coding scheme (MCS) for the SU data portionand the signal-B field of the MU-type PPDU includes a MCS for the MUdata portion.
 9. The device of claim 6, wherein the signal-B field ofthe MU-type PPDU includes partial association identifiers (AIDs)identifying the plurality of receivers.
 10. The device of claim 6,wherein the signal-A field of the SU-type PPDU includes information on anumber of spatial streams assigned to the receiver and the signal-Bfield of the MU-type PPDU includes information on a number of spatialstreams assigned to the plurality of receivers.